One or more embodiments relate to a method of programming a nonvolatile memory device.
Recently, there is an increasing demand for nonvolatile memory devices which can be electrically programmed and erased and do not require the refresh function of rewriting data at specific periods.
A nonvolatile memory cell enables electrical program/erase operations and performs the program and erase operations through a threshold voltage variation when electrons are migrated by a relatively strong electric field applied to a thin oxide layer.
The nonvolatile memory device typically includes a memory cell array in which cells for storing data are arranged in a matrix form and a page buffer for writing data into specific cells of the memory cell array or reading data stored in specific cells thereof. The page buffer includes bit line pairs connected to specific memory cells, a register for temporarily storing data to be written into the memory cell array or reading the data of specific cells from the memory cell array and temporarily storing the read data, a sensing node for detecting the voltage level of a specific bit line or a specific register, and a bit line select unit for controlling whether to connect the specific bit line to the sensing node.
It has been known that the program speed of a nonvolatile memory device increases as the number of program/erase cycles increases. This is because, with the increasing number of program/erase cycles, electric charges trapped at the floating gate of each of the memory cells increase, so the threshold voltage of each cell increases. Accordingly, although a relatively small program pulse is applied to the cell using an Incremental Step Pulse Program (ISPP) method, the cell may be programmed to have a target threshold voltage or a larger voltage.
A method of setting and applying a low program start voltage in the ISPP method may be taken into consideration. If this method is used when the number of program/erase cycles is relatively small, the time for performing an operation increases. This is because, with a lower program start voltage, the number of pulses to be applied increases.